The present invention relates to an apparatus for separating materials such as a thickening or dewatering apparatus and to a method of separating, thickening or dewatering a solids/liquid mixture, such as a slurry.
Many industries such as mining, water treatment and pollution control produce slurries which need to be thickened or dewatered for either further treatment or disposal as waste.
Dewatering of slurries can be divided up into three types of processes. These are as follows:
gravity separation; mechanical using vacuum, pressure filters and centrifuges; and thermal. PA1 a main body PA1 a rotor disposed within said main body, said rotor and said main body being rotatable about axes of rotation; said rotor comprising: PA1 feeding material to a rotatable rotor which forms a series of sub-chambers; PA1 causing rotation of the rotor to separate material within the sub-chambers into lighter and heavier components; PA1 transferring the heavier component through the sub-chambers from an inlet end to an outlet end; and PA1 discharging the lighter and heavier components from the sub-chambers. PA1 an external barrel; and PA1 a rotor adapted to rotate about an axis of rotation within said barrel; wherein PA1 said rotor comprises: PA1 rotating, about an axis of rotation within a chamber having a feed end and an axially displaced discharge end, a rotor, said rotor comprising substantially radial blades extending substantially axially therealong between said inlet end and said outlet end; PA1 feeding a slurry to be thickened or dewatered around the periphery of said rotor at the feed end of said chamber into a sludge blanket formed in said chamber by the rotation of said rotor; and PA1 causing said thickened or dewatered slurry to travel from said feed end to said discharge end along or adjacent the circumference of said rotor, to be discharged from said chamber adjacent the circumference of said rotor, while said liquor separated from said thickened or dewatered slurry discharges from a central axially located outlet in said discharge end of said chamber.
Each increasing level of dewatering result in a higher unit cost of solids treated.
Conventionally slurries are thickened in large circular thickener tanks (see FIG. 1) where the solids are introduced so as to provide a "top entry" path A and allowed to settle by gravity, often with the use of flocculating agents, to the bottom of the tank where they are withdrawn, with the clarified fluids being drawn off the surface periphery usually by surface weirs.
A development of this process has occurred over the past two decades with the utilization of a sludge blanket or submerged feed entry A into the thickener (see FIG. 2).
This process has increased in utilization by the recent development of high molecular weight flocculants, which have resulted in the reduction of up to 75% in the surface area of the thickener.
These treated slurries can then be fed to more expensive treatment devices such as centrifuges, filtration means or thermal means. However, because of cost limitations some slurries are only treated by gravity means.
Centrifuges are generally as shown in FIG. 3. Normally, flocculated feed is introduced into the centrifuge (1), by a "top entry" path (2) through a region of high shear. This region of high shear requires high usage of flocculant at considerable expense. Top entry of the feed, as in conventional thickeners, utilizes none of the sludge blanket effect and hence, as in conventional tank thickeners, requires a larger residence time to achieve the required results.
Current centrifuges (1) are primarily designed to process solids, with little consideration being given to the flow of the liquor or centrate, which is required to follow a very convoluted path through the scroll (3) to the liquid outlet (4) in the form of a weir (5). This system results in increased turbulence and interaction between the centrate and the settled solids; relying on the high centrifugal forces created by the machine to produce acceptable separation.